Abstract
The 2013 multistate outbreaks contributed to the largest annual number of reported US cases of cyclosporiasis since 1997. In this paper we focus on investigations in Texas. We defined an outbreak-associated case as laboratory-confirmed cyclosporiasis in a person with illness onset between 1 June and 31 August 2013, with no history of international travel in the previous 14 days. Epidemiological, environmental, and traceback investigations were conducted. Of the 631 cases reported in the multistate outbreaks, Texas reported the greatest number of cases, 270 (43%). More than 70 clusters were identified in Texas, four of which were further investigated. One restaurant-associated cluster of 25 case-patients was selected for a case-control study. Consumption of cilantro was most strongly associated with illness on meal date-matched analysis (matched odds ratio 19·8, 95% confidence interval 4·0-∞). All case-patients in the other three clusters investigated also ate cilantro. Traceback investigations converged on three suppliers in Puebla, Mexico. Cilantro was the vehicle of infection in the four clusters investigated; the temporal association of these clusters with the large overall increase in cyclosporiasis cases in Texas suggests cilantro was the vehicle of infection for many other cases. However, the paucity of epidemiological and traceback information does not allow for a conclusive determination; moreover, molecular epidemiological tools for cyclosporiasis that could provide more definitive linkage between case clusters are needed.
Highlights
Cyclospora cayetanensis is the protozoan parasite that causes cyclosporiasis
In the United States, at least one third of non-outbreak-associated cyclosporiasis cases have been associated with international travel [2]
We report the results as odds ratios (ORs) with corresponding 95% confidence intervals (CIs); we provide a median unbiased estimate of the OR if the upper bound of the CI is infinity
Summary
Cyclospora cayetanensis is the protozoan parasite that causes cyclosporiasis. Cyclosporiasis is characterized by profuse watery diarrhoea; anorexia, fatigue, weight loss, nausea, flatulence, abdominal cramping, myalgia, vomiting, and low-grade fever may occur [1]. In the United States, at least one third of non-outbreak-associated cyclosporiasis cases have been associated with international travel [2]. C. cayetanensis is not directly transmitted from one person to another; an infected person sheds unsporulated oocysts in the faeces, which are non-infective. These oocysts do not multiply outside the human host and require days to weeks in the environment to become infective [5]. In the United States, most of the reported cases have occurred during May–August, peaking in June and July [1, 2]
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